Filter bags for vacuum cleaners which have a tubular bag and, as well as a closed free end area, a folded bottom, a so-called “square bottom”, are known in the prior art. Usually such dust bags are produced from a paper material which can be processed on standard tubular bag systems. In the case of such filter bags, an appropriate retaining plate is generally attached to the square bottom and has an opening through which the air to be cleaned is led. The task of the square bottom is to stabilise the filter bag and form a three-dimensional bag. Moreover the square bottom makes it easier to fit the bag into the vacuum cleaner.
Recently however, new developments have become known in respect of materials for vacuum cleaner bags. Thus the document WO 01/03802 A1 describes a special non-woven material comprising a plurality of plies of filter material which are independent of one another. These independent plies are connected to form a filter material which has special properties. In practice it has become apparent that vacuum cleaner bags which are produced from such a non-woven material are considerably superior to previously known bags in respect of the efficiency of the vacuum cleaner.
As a result of this bag material being low in flexural strength however, the formation of a square bottom is only possible with difficulty or with great outlay.
The document DE 100 64 608 A1 describes a solution for securing a retaining plate to such a bag. According to this document, first a tubular arrangement of the vacuum cleaner bag is undertaken with the formation of a fold along a longitudinal edge. This tubular arrangement is then separated, such that a second end area is produced. The opposite free ends of such a tubular arrangement are closed and a retaining plate is allocated to an end area after an appropriate opening has been formed. According to the teaching of DE 100 64 608 A1, a special fold is then made in the area of the vacuum cleaner bag between the area provided with the retaining plate and the free end. Stabilisation of the bag which is of low flexural strength is intended to be achieved by means of the special design of transverse folds.
The method described in DE 100 64 608 A1 is very expensive however.
In the document EP 1 059 056 A1 is described a further solution for introducing a retaining plate for a bag into the filter material. According to the solution proposed by EP 1 059 056 A1, two independent plies of the filter material are guided on top of one another and welded together in the edge areas. Subsequently, the welded material is separated and the two open transverse sides are welded together. For introducing a retaining plate, an appropriate hole is stamped into the superposed plies and a reinforcement is laid around the two plies.
What is disadvantageous about this solution is that no bottom is formed here which stabilises the bag per se, but that a reinforcing means, i.e. a retaining plate, must always inevitably be attached. The retaining plate, which is attached according to the above-mentioned European application, must in addition always be foldable since it is laid around the two plies which are placed on top of one another. Thus this bag is subject to great restrictions in relation to its application in the field of vacuum cleaners, since the retaining plate regularly has to fulfill a plurality of functions. With retaining plates it has namely been usual up to now to attach in addition slides or flaps with which the opening can be sealed for the hygienic removal of the vacuum cleaner bag. This is not possible with a foldable embodiment of the retaining plate. It is also not possible to attach the retaining plate e.g. on the longitudinal sides of the bag since there is no bottom present to stabilise the bag.